The Janome and Bernina bobbins are the same in height and width. But the Bernina bobbin center hole is a little tighter. You can tell them apart by how many holes are in them. The Bernina ones have 7 holes, and the "class 15" bobbins have 10 holes. The 10-hole bobbin work in a lot of different machines. But as you've discovered, the Bernina ones will work in other machines, they just can't be wound on other brand bobbin winders.